When a person needs a hearing aid, the hearing aid should be configured to the specific hearing ability of that person. Specifically the hearing ability may include hearing loss. There are several ways of determining the hearing ability of a person. The most common method is pure-tone audiometric for determining hearing thresholds at selected frequencies. A model may then be established using the measurement results. Also hearing ability of a person without a hearing loss may be determined so as to improve or enhance hearing for that person.
The threshold of hearing is one of the most important clinical variables for characterizing a person's hearing ability profile, since it indicates the weakest acoustic signal that the person is able to hear. Specifically the person's hearing ability profile may provide information on the weakest acoustic signal a person is able to hear as a function of frequency. Because hearing ability, and specifically hearing loss, results may have significant influence on educational, occupational, social, and/or psychological outcome it is advantageous that procedures may be standardized and consistent among test providers. Since early days, starting with Fechner's method of limits, several pure-tone audiometric measurement procedures have been proposed to estimate a person's hearing threshold.
Three general methods of pure tone audiometry are used namely (a) manual audiometry, (b) automatic audiometry, also known as Békésy audiometry; and (c) computer-assisted audiometry.
Békésy audiometry refers to a method where the listener himself controls the loudness of a frequency-sweeping stimulus so as to follow his own hearing threshold as close as possible. Manual threshold measurement procedures put the audiologist in control of the stimulus presentation schedule. The currently recommended manual pure-tone threshold estimation method relies on an ascending technique with 5 dB up and 10 dB down steps, (see the ASHA Guidelines for manual pure-tone threshold audiometry, 2005). Lately, computer-assisted procedures that implement popular manual and automatic procedures have become commercially available, such as the MADSEN Astera.
In addition to pure tone audiometry with a manual yes/no response, given e.g. as a sign to an audiologist or as a press on a button, indicating the ability of the person tested to hear a tone, variations of testing the hearing ability of a person exist both in the type of stimulation and in the observation of responses.
Sound transmitted in one ear may be conducted in the cranium bone and may be heard in the other ear, especially in the case where the hearing loss differs very much between the ears. In this case the stimulus may be required to comprise additional masking noise in the ear not tested, which is intended to reduce the risk of the person tested responding to sound transmitted to the other ear. To provide diagnosis of the source of a hearing loss, stimulus may also be transmitted via bone conduction as vibration rather than as air conducted sound. In this case masking becomes even more relevant. In the case of masked pure tones, the power level of the masking noise must be balanced correctly. Therefore such a masked test of hearing ability will have a longer duration.
In addition to using pure tones as stimulus, a combination of speech and noise may also be used to identify the speech hearing and/or speech recognition ability of the person tested. In this case the response may also be more complex in choosing between several potential words.
Especially for infants, unable to respond by pressing a button, recording responses in the form of the electrical potential measured on the scalp of a person tested (e.g. EEG) is also used as observations of responses. Various variations of this concept exist, for instance ABR (auditory brainstem response)—where an audiologist manually observes whether a curve shows a response to either click sounds for a simple evaluation of hearing ability, or alternatively whether the curve shows a response to pure tone stimulus similar to that in normal pure tone audiometry with the aim of estimating frequency dependent hearing thresholds, also ASSR (auditive steady state response) where frequency and/or amplitude modulated tone stimulus is correlated to responses in the form of EEG curves by statistical techniques.
Patent publication WO2007/042043 to GN ReSound provides information relating to Bayesian statistics background.
Ozdamar et al. (Journal of the Acoustical Society of America, 1990; 88:2171-9), proposed CAST (classification of audiograms by sequential testing) developed as an automated approach to screening infant hearing abilities using a modified Bayesian method. In contrast to the embodiments described herein, the CAST method is based on traditional recording of an audiogram, and after the test categorizing this according to a predefined discrete set of template audiograms. Furthermore, a new audiogram is assigned a posterior membership to a set of template audiograms incrementally.
A first aspect of the embodiments described herein relates to a method of establishing a hearing ability model for a person. The method may include providing a representation of the distribution of hearing ability for a population of individuals and the method may comprise the steps:                i) performing a hearing evaluation event, comprising a stimulus of a person tested and a conscious or subconscious response of the person tested,        ii) registering an observation related to the response of the hearing evaluation event,        iii) establishing a hearing ability model representing the hearing ability of the person tested, based on the observation related to the hearing evaluation event and the representation of the distribution of the hearing ability.        
Surprisingly the method above provides a model of the hearing ability of a person significantly faster than other methods as will be discussed below. In addition to that the method may provide an associated uncertainty of the model. The term faster may be construed as a shorter period of time where person is under active testing. The term faster may be also construed as a lower number of hearing evaluation events. One objective is to provide a method where the person is subjected to less discomfort while performing a hearing ability evaluation test.
The response of the person may be conscious and/or subconscious. E.g. the person may operate a switch and/or an electric signal in/from the brain may be registered.
The model may comprise an initial step of determining an initial model based on the representation of the distribution of hearing ability for a population of individuals and the first iteration of the method may include determining hearing ability model representing the hearing ability of the person tested based on the observation related to the hearing evaluation event and the initial model. Each subsequent iteration may include determining an updated model based on the latest hearing ability model and the latest, or set of latest, observations.
One object of the embodiments is to establish a sufficiently accurate estimate of the hearing threshold while limiting the burden on the person tested and/or the audiologist. In practice, this means that the “true” hearing threshold should be reached through a minimal number of listening experiments.
A second aspect of the present embodiments relates to a system for establishing a hearing ability model of the hearing ability of a person. The system may comprise:                a data storage configured to store a representation of the distribution of the hearing ability of a population of individuals representing distribution of hearing ability of a multitude of hearing impaired individuals,        a hearing evaluation device configured to provide a stimulus relating to a hearing evaluation event,        an observation registering device configured to register a response related to the hearing evaluation event,        a processor configured to establish a hearing ability model of the person tested based on the response related to the hearing evaluation event and the data set.        
As with the above method the system according to the second aspect surprisingly provides a model of the hearing ability of a person by using few hearing evaluation events compared to other methods. This is contemplated to reduce the discomfort for a person being tested. This may be advantageous for any person and in particular, but not limited to, children and elderly persons. Other advantages will be obvious from the description below.
Further, the distribution of the hearing ability of a population of individuals may be stored as a data set or as a mathematical model or in any other appropriate way.
In accordance with some embodiments, a method of establishing a hearing ability model for a person using a representation of a distribution of hearing ability for a population of individuals, includes obtaining information regarding a person's response to a stimulus of a hearing evaluation event, and establishing, using a processor, a hearing ability model representing a hearing ability of the person, based at least in part on the information and the representation of the distribution of the hearing ability for the population.
In accordance with other embodiments, a system for establishing a hearing ability model of a hearing ability of a person, includes a data storage configured to store a representation of a distribution of a hearing ability of a population of individuals, and a processor configured to establish a hearing ability model representing a hearing ability of the person based at least in part on (i) information regarding a person's response to a stimulus of a hearing evaluation event, and (ii) the representation of the distribution of the hearing ability of the population.
In accordance with other embodiments, a system for establishing a hearing ability model of a hearing ability of a person, includes a data storage configured to store a representation of a distribution of a hearing ability of a population of individuals, a response observation device configured provide information regarding a person's response to a stimulus of a hearing evaluation event, and a processor configured to establish a hearing ability model representing a hearing ability of the person based at least in part on the information and the representation of the distribution of the hearing ability of the population.
In accordance with other embodiments, a system for establishing a hearing ability model for a person using a representation of a distribution of hearing ability for a population of individuals, includes means for obtaining information regarding a person's response to a stimulus of a hearing evaluation event, and means for establishing a hearing ability model representing a hearing ability of the person, based at least in part on the information and the representation of the distribution of the hearing ability for the population.